Rabioreceiver



g- 27, 1929- N. ASHBRIDGE 1,725,949

mnzomacmvsn Filed June 24, 1924 TO QMPHFIERS NOEL ASHBRIDGE INVENTOR TORNEY Patented Aug. 27, 1929.

UNITED STATES PATENT OFFICE.

NOEL ASHBRIDGE, F WANSTEAD, ENGLAND, ASSIGNOR TO RADIO CORPORATION OF AMERICA, A CORPORATION OF DELAWARE.

RADIORECEIVER.

Application, filed June 24, 1924, Serial No The object of this invention is to produce a receiver which, on the one hand, convenient for quick searching, and, on the other hand, can employ tuned high frequency amplification with its attendant increase of signal strength and selectivity. In most receivers which use the well known tuned anode circuit good results are obtained as regards both strength of signal and selectivity, but such receivers have certain disadvantages, the most important being that when it is required to pick up a station whose wave length is unknown, it is necessary, while searching, to keep the two circuits very closely in tune. Again considerable diificulty is usually e1:-

perienced when it becomes necessary to change over quickly from one wave length to another, especially of course when the wave length is not known in advance. A further diliiculty 2 arises in connection with the provision of reaction to give effect both on the aerial and .anode circuits, and at the same time to be suitable for a large wave range and widely varying conditions of reception. The pres ent invention obviates these dlfl'lCLlltlGS to a very large degree.

According to this invention I employ a rectifying valve with reaction coupling to the aerial and a high frequency amplifying valve, the grid of which is connected to the high potential end of the tuning inductance. An oscillatory circuit is included in the plate circuit of the second valve. There is also a detector valve, the grid of which is connected to the plate of the second valve through a condenser. The plate of the detector valve is connected to the low potential end of the reaction coil and to one end of the primary winding of an output transformer, which winding may form part of the plate circuit of the first valve.

The invention is illustrated by the accompanying diagram. The grid and filament of a valve A are'connected across the aerial tuning inductance 'L which in conjunction with C forms an aerial tuning system. C may of course be connected in parallel with the inductance L or inseries with it. A grid leak R and condenser C are connected in the grid circuit of this first valve to produce rectification. The anode circuit of the valve A consists of a reaction coil L and intervalve transformer primary F and of course high 721,990, and in Great Britain July 2, 1923.

tension supply. The primary P is common to the plate circuit of the valve A and to that of the detector valve C and is shunted by a condenser G to by-pass any high frequency flowing in this circuit. The grids of valves A and B are connected to the high potential end of the aerial. tuning inductance L The plate circuit of the valve B includes the tuned anode or tuned high frequency circuit L G and is completed to earth through the high tension battery. Connection is made from the anode of valve B through a condenser C to the grid of valve C. A resistance R of the order of half a megohm'is connected between the grid of valve 0 and earth. The secondary N of the intervalve transformer may be connected to the grid and filament of an amplifying valve. A telephone transformer or a pair of high resistance telephones may be substituted for the inter-valve transformer. I

The method of using this circuit is as follows 7 If it is desired to pick up a station whose wave length is not accurately known, the filaments of the valves B and C are switched off, and the valve A is used. When the station has been found, in order to introduce the tuned high frequency amplification valve B with its associated detector valve C all that is necessary is to complete the filament circuits of these valves, the important point being that no switching of any high frequency portion of the circuit is necessary. When these valves are switched on it will be found that whatever may be the tuning of the anode tuned circuit the signal as received on the stand-by arrangement will not be lostalthough it will be slightly weaker owing to the extra loading of the grid of the valve B. All that is then necessary is to tune the circuit L C until either the system oscillates or an increase of signal strength is noted.

The question as to whether the receiver will oscillate when L C is brought into tune with D. C depends largely upon the ratio of C/L in the tuned anode circuit. If this ratio is large the signal will be increased without oscillations commencing. If the ratio is small. immediately the two circuits come in tune the receiver will for the moment oscillate. All that is nceessary to stop this is to weaken slightly the reaction coil coupling between L and L This reaction coil is arranged so that it will rotate through 180 degrees, so that in cases where the ratio C/L in the circuit L C is extremely small, it will be necessary to use a very slight amount of reversed reaction in order to stop continuous oscillations. This reversed reaction is, of course, necessary to counterbalance some of the capacity reaction which is always present in these circuits due to the inter-electrode capacity in valve B. It would be possible to arrange a permanent reversed capacity reaction so that when switching in valves B and C the reaction point remains the same as that necessary when receiving without the valves B and C, but this sacrifices a certain amount of sensitivity owing to the fact that under these conditions it is not possible to eliminate so much of the resistance in the tuned anode circuit. Any value of O and L desired may be used in the circuit L C and although this will vary the amount of reaction necessary, it will not do so to anything like the extent that is normally the case when reaction is directly associated with the valves B or G. Thus it will be seen that for the purpose of obtaining elimination of jamming very high C/L ratios may be used in I 0 Again the circuit may also be arranged with very small ratios of C/L, in which case maximum amplification is obtained. In either case the reaction obtained from the valve A will give control up to and beyond the oscillation point. Thus it will be seen that the invent-ion provides a receiver with which it is very easy to search and then to switch over to a selective arrangement with increased signal strength without losing the signal during the process. This condition is, of course, not possible with the normal arrangement of coupled circuit. As al ready stated this operation can be carried out without switching any part of the high frequency circuits, which is very important when dealing with short wave lengths. It

will be noticed that when all the valves are in operation the primary P of the inter-valve transformer carries two components of low frequency current, one being supplied by the rectified current in the plate circuit of the valve A, the other by the rectified current in the plate circuit of the valve C. It is found in practice that the effect of these two components tends to increase very slightly the strength of signal, although the extra signal strength obtained from the valve A due to this condition is negligible.

In place of connecting the plate of valve A to the positive pole of the high tension battery through the winding I I may connect it directly to that pole, but the signal is lost when switching in the high frequency valve until the high frequency circuit has been tuned to the incoming signal.

I have found that a receiver constructed in accordance with this invention is suitable for use in duplex telephony.

Having described my invention what I claim is 1. In a radio receiver the combination of a three-electrode valve having input and output circuits connected by an inductively coupled feedback, a second three-electrode valve having an input circuit and an output circuit tuned to the incoming signal frequency, a single source of received oscillations coupled to the input of each of said valves and an impedance common to the output circuits of said valves.

2. In a radio receiver the combination of a three-electrode rectifying valve havin input and output circuits interlinked to produce feedback, a second three-electrode valve having tuned input and output circuits, a third three-electrode valve having its input circuit coupled to the output circuit of the second valve, a single source of received oscillations connected. to the input circuits of the first and second valves and an impedance common to the output circuits of the first and third valves.

3. In a radio receiver the combination of a three-electrode rectifying valve and input and output circuits interlinked by an inductively coupled feedback, a second three-elem trode valve having input and output circuits, said output circuit being tuned to the signal frequency, a third three-electrode valve having its input coupled to the output circuit of the second valve, a source of received oscillations connected to the input circuits of the first and second valves and a transformer having one of itswindings common to the output circuits of the first and third valves.

4;. In a radio receiver the combination of a three-electrode valve and input and output circuits connected by an inductiviely coupled feedback, a second three-electrode valve having an input and a'tuned output circuit, a third three electrode valve having its input circuit coupled to the output circuit of the second valve, the anode of said third valve being connected to the low potential end of the feedback coil of the first valve, a source of received oscillations coupled to the input of each of said first and second named valves and a coil common to the output circuits of the first and third valves.

5. A radio receiver comprising an aerial having an inductance, a rectifier having cathode, grid and anode and an output circuit having feedback connection to said inductance, an amplifier valve having cathode, grid and anode, a circuit connecting the grids of said rectifier and said amplifier, an output circuit connected to the anode and cathode of said amplifier and control means for initiating electronic flow in said amplifier.

6. In a radio receiver the combination of a three electrode valve having its input and output circuits coupled by an inductively coupled feed back, a second three electrode valve having input and output circuits, said output circuit having means for tuning to the signal frequency, a single source of received oscillations having means for tuning to a desired frequency, said source being coupled with the input of each of said valves and an impedance common to the output circuits of said valves whereby the signals of the desired frequency amplified by both valves may be combined therein.

7. In a radio receiver, the combination of a three electrode rectifying valve having input and output circuits coupled by an inductively coupled feedback, a second three electrode valve having input and output circuits said output circuit including tuning means tuned to the incoming signal frequency, a single source of received oscillations having means for tuning it to the signal frequency, said source being coupled with the input of each of said valves and a coil included in the outputs of each of said valves.

8. In a radio receiving system the combination of an input circuit adapted to be tuned to a desired signal frequency and two three-electrode valves with their associated input and output circuits, each of said valves having its input electrode connected with the tuned source, one of said valves having an inductive feed-back between its input and output circuits and the other of said valves having its plate circuit tuned for production of internal feed back, means for detecting currents of each of said valves and means for combining said detected currents.

9. In a radio receiving system the combination of a three-electrode valve having interlinked input and output circuits, a second three electrode valve having an input circuit and an output circuit including an oscillating circuit tuned to the signal frequency, a third three-electrode valve having its input circuit coupled to the output circuit of the second valve, a source of received oscillations coupled to the input circuits of the first and second valves, an impedance common to the output circuits of the first and third valves and means for initiating electronic flow in the second and third valves, whereby the current thru said impedance is the output current of the first valve alone when the second and third valves are inactive and is the sum of the output currents of the first and third valves when the second and third valves are active.

NOEL ASHBRIDGE. 

